Electron beam columns are well known in the art. FIG. 1 is a diagram of a conventional shaped beam column 10, such as used in a conventional electron beam lithography tool that images a focused shape, defined by an aperture, onto a writing plane. Column 10 includes a low brightness electron source 12, such as a tungsten or LaB.sub.6 thermionic emitter, (e.g., with 10-20 .mu.m (micrometer) crossover), that produces an electron beam 13 that is converted into flood illumination 14 via an aperture 16 and electron beam lens 18, as is well understood in the art. Flood illumination 14 is projected on a square shaped aperture 20. A series of electron beam lenses 22 and 24, which may be magnetic lenses or electrostatic lenses, are used to focus the electrons passing through square shaped aperture 20 and project a demagnified image of square shaped aperture 20 on a writing plane 26. When column 10 is used as a lithography tool, writing plane 26 may be the surface of a mask blank or resist on the wafer.
As shown in FIG. 1, conventional shaped electron beam column 10 produces a focused image of square shape aperture 20 on writing plane 26. Typically, the size of square shaped aperture 20 used in column 10 is small and the image of square shaped aperture 20 on writing plane 26 is produced with a large total linear column demagnification. For example, where square shaped aperture 20 is 10.times.10 .mu.m, a total linear column demagnification of 100 is needed to form a 100.times.100 nm (nanometer) image of square shaped aperture 20 on writing plane 26.
Column 10 generally uses a number of electron beam lenses to generate the desired large total linear column demagnification. The use of multiple electron beam lenses, however, results in a large column length. For example, conventional column 10 typically has a length of approximately 50 cm (centimeter). Unfortunately, the large length of column 10 creates a large amount of electron-electron interactions. As is well understood by those having ordinary skill in the art, electron-electron interactions decrease the edge resolution of the image projected on writing plane 26 resulting in edge blur of the image. This decreases the current that can be used in column 10, which decreases the throughput of column 10 when used for electron beam lithography.
In a conventional column it is desirable to have an edge blur of less than approximately twenty five percent of the minimum size image. For example, if column 10 should generate an image with approximate dimensions of 100.times.100 nm, the image will have an approximately 25 nm edge blur.